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CSC358 Week 12
Adapted from slides by J.F. Kurose and K. W. Ross.All material copyright 1996-2016 J.F Kurose and K.W. Ross, All Rights Reserved
Logistics
§ Today:• Finishing ”wireless and mobile”• Exam review
§ Tomorrow• Tutorial
§ Pre-exam office hours next week• Monday, Wednesday, Friday: 3-5 PM
Network Layer 4-2
We are here
4-3
Outline
7.1 Introduction
Wireless7.2 Wireless links,
characteristics• CDMA
7.3 IEEE 802.11 wireless LANs (�Wi-Fi�)
7.4 Cellular Internet access• architecture• standards (e.g., 3G,
LTE)
Mobility7.5 Principles: addressing and
routing to mobile users7.6 Mobile IP7.7 Handling mobility in
cellular networks
7-4Wireless and Mobile Networks
Mobile Switching
Center
Public telephonenetwork
Mobile Switching
Center
Components of cellular network architecture
v connects cells to wired tel. net.v manages call setup (more later!)v handles mobility (more later!)
MSC
v covers geographical regionv base station (BS) analogous to 802.11 APv mobile users attach to network through BSv air-interface: physical and link layer protocol between mobile and BS
cell
wired network
7-5Wireless and Mobile Networks
BSCBTS
Base transceiver station (BTS)
Base station controller (BSC)
Mobile Switching Center (MSC)
Mobile subscribers
Base station system (BSS)
Legend
2G (voice) network architecture
MSCPublic telephonenetwork
GatewayMSC
G
7-6Wireless and Mobile Networks
3G (voice+data) network architecture
radionetwork controller
MSC
SGSN
Public telephonenetwork
GatewayMSC
G
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
Public Internet
GGSN
G
Key insight: new cellular datanetwork operates in parallel(except at edge) with existing cellular voice network§ voice network unchanged in core§ data network operates in parallel
7-7Wireless and Mobile Networks
4G: differences from 3G
§ all IP core: IP packets tunneled (through core IP network) from base station to gateway
§ no separation between voice and data – all traffic carried over IP core to gateway
radio access networkUniversal Terrestrial Radio Access Network (UTRAN)
Evolved Packet Core(EPC)
Public Internet
P-GW
G
S-GW
G
UE(user element)
eNodeB(base station)
Packet data networkGateway(P-GW)
Serving Gateway(S-GW)
data
MMEHSS
Mobility Management Entity (MME)
control
Home Subscriber Server(HSS)
7-8Wireless and Mobile Networks
Outline
7.1 Introduction
Wireless7.2 Wireless links,
characteristics• CDMA
7.3 IEEE 802.11 wireless LANs (�Wi-Fi�)
7.4 Cellular Internet Access• architecture• standards (e.g., 3G, LTE)
Mobility7.5 Principles: addressing
and routing to mobile users
7.6 Mobile IP7.7 Handling mobility in
cellular networks
7-9Wireless and Mobile Networks
What is mobility?
§ spectrum of mobility, from the network perspective:
no mobility high mobility
mobile wireless user, using same access point
mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)
7-10Wireless and Mobile Networks
mobile user, connecting/ disconnecting from network using DHCP.
wide area network
Mobility: vocabularyhome network: permanent �home� of mobile(e.g., 128.119.40/24)
permanent address:address in home network, can always be used to reach mobilee.g., 128.119.40.186
home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote
7-11Wireless and Mobile Networks
Mobility: more vocabulary
wide area network
care-of-address: address in visited network.(e.g., 79,129.13.2)
visited network: network in which mobile currently resides (e.g., 79.129.13/24)
permanent address: remains constant (e.g., 128.119.40.186)
foreign agent: entity in visited network that performs mobility functions on behalf of mobile.
correspondent: wants to communicate with mobile
7-12Wireless and Mobile Networks
How do you contact a mobile friend:
I wonder where Alice moved to?
Consider friend frequently changing addresses, how do you find her?
7-13Wireless and Mobile Networks
Mobility: approaches§ let routing handle it: routers advertise permanent
address of mobile-nodes-in-residence via usual routing table exchange.• routing tables indicate where each mobile located• no changes to end-systems
§ let end-systems handle it: • indirect routing: communication from
correspondent to mobile goes through home agent, then forwarded to remote
• direct routing: correspondent gets foreign address of mobile, sends directly to mobile
7-14Wireless and Mobile Networks
Mobility: approaches
§ let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange.• routing tables indicate where each mobile located• no changes to end-systems
§ let end-systems handle it: • indirect routing: communication from
correspondent to mobile goes through home agent, then forwarded to remote
• direct routing: correspondent gets foreign address of mobile, sends directly to mobile
7-15Wireless and Mobile Networks
not scalable
to millions ofmobiles
wide area network
Mobility: registration
end result:§ foreign agent knows about mobile§ home agent knows location of mobile
home networkvisited network
1
mobile contacts foreign agent on entering visited network
2
foreign agent contacts home agent home: �this mobile is resident in my network�
7-16Wireless and Mobile Networks
Mobility via indirect routing
wide area network
homenetwork
visitednetwork
3
24
1correspondent addresses packets using home address of mobile
home agent intercepts packets, forwards to foreign agent
foreign agent receives packets, forwards to mobile
mobile replies directly to correspondent
7-17Wireless and Mobile Networks
Indirect Routing: comments§ mobile uses two addresses:• permanent address: used by correspondent (hence
mobile location is transparent to correspondent)• care-of-address: used by home agent to forward
datagrams to mobile
§ triangle routing: correspondent-home-network-mobile• inefficient when correspondent, mobile are in same network
7-18Wireless and Mobile Networks
Indirect routing: moving between networks
§ suppose mobile user moves to another network• registers with new foreign agent• new foreign agent registers with home agent• home agent update care-of-address for mobile• packets continue to be forwarded to mobile (but
with new care-of-address)§ mobility, changing foreign networks transparent to
end hosts: on going connections can be maintained!
7-19Wireless and Mobile Networks
1 23
4
Mobility via direct routing
homenetwork
visitednetwork
correspondent requests, receives foreign address of mobile
correspondent forwards to foreign agent
foreign agent receives packets, forwards to mobile
mobile replies directly to correspondent
7-20Wireless and Mobile Networks
Mobility via direct routing: comments
§ overcome triangle routing problem§ non-transparent to correspondent: correspondent
must get care-of-address from home agent• what if mobile changes visited network?
1 23
4
7-21Wireless and Mobile Networks
wide area network
1
foreign net visited at session start
anchorforeignagent 2
4
new foreignagent
3
correspondentagent
correspondent
new foreignnetwork
Accommodating mobility with direct routing§ anchor foreign agent: FA in first visited network§ data always routed first to anchor FA§ when mobile moves: new FA arranges to have
data forwarded from old FA (chaining)
5
7-22Wireless and Mobile Networks
Outline
7.1 Introduction
Wireless7.2 Wireless links,
characteristics• CDMA
7.3 IEEE 802.11 wireless LANs (�Wi-Fi�)
7.4 Cellular Internet Access• architecture• standards (e.g., 3G, LTE)
Mobility7.5 Principles: addressing and
routing to mobile users7.6 Mobile IP7.7 Handling mobility in
cellular networks
7-23Wireless and Mobile Networks
Mobile Internet Protocol
§ RFC 3344§ has many features we’ve seen: • home agents, foreign agents, foreign-agent registration,
care-of-addresses, encapsulation (packet-within-a-packet)
§ three components to standard:• indirect routing of datagrams• agent discovery• registration with home agent
7-24Wireless and Mobile Networks
Mobile IP: indirect routing
Permanent address: 128.119.40.186
Care-of address: 79.129.13.2
dest: 128.119.40.186
packet sent by correspondent
dest: 79.129.13.2 dest: 128.119.40.186
packet sent by home agent to foreign agent: a packet within a packet
dest: 128.119.40.186
foreign-agent-to-mobile packet
7-25Wireless and Mobile Networks
Mobile IP: agent discovery
§ agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9)
RBHFMGV bits reserved
type = 16
type = 9 code = 0 = 9
checksum = 9
router address standard
ICMP fields
mobility agent advertisement
extension
length sequence #
registration lifetime
0 or more care-of-addresses
0 8 16 24
R bit: registration required
7-26Wireless and Mobile Networks
Mobile IP: registration examplevisited network: 79.129.13/24
home agentHA: 128.119.40.7
foreign agentCOA: 79.129.13.2
mobile agentMA: 128.119.40.186
registration req. COA: 79.129.13.2HA: 128.119.40.7MA: 128.119.40.186identification:714….
registration reply HA: 128.119.40.7MA: 128.119.40.186Identification: 714….
registration reply HA: 128.119.40.7MA: 128.119.40.186Identification: 714….
time
ICMP agent adv.COA: 79.129.13.2….
registration req. COA: 79.129.13.2HA: 128.119.40.7MA: 128.119.40.186identification: 714….
7-27Wireless and Mobile Networks
Outline
7.1 Introduction
Wireless7.2 Wireless links,
characteristics• CDMA
7.3 IEEE 802.11 wireless LANs (�Wi-Fi�)
7.4 Cellular Internet Access• architecture• standards (e.g., 3G, LTE)
Mobility7.5 Principles: addressing and
routing to mobile users7.6 Mobile IP7.7 Handling mobility in
cellular networks
7-28Wireless and Mobile Networks
Components of cellular network architecture
correspondent
MSC
MSCMSC MSC
MSC
wired public telephonenetwork
different cellular networks,operated by different providers
recall:
7-29Wireless and Mobile Networks
Handling mobility in cellular networks
§ home network: network of cellular provider you subscribe to (e.g., Rogers, Bell, Verizon)• home location register (HLR): database in home network
containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network)
§ visited network: network in which mobile currently resides• visitor location register (VLR): database with entry for
each user currently in network• could be home network
7-30Wireless and Mobile Networks
Public switched telephonenetwork
mobileuser
homeMobile
Switching Center
HLR home network
visitednetwork
correspondent
Mobile Switching
Center
VLR
GSM: indirect routing to mobile
1 call routed to home network
2
home MSC consults HLR,gets roaming number ofmobile in visited network
3
home MSC sets up 2nd leg of callto MSC in visited network
4
MSC in visited network completescall through base station to mobile
7-31Wireless and Mobile Networks
Mobile Switching
Center
VLR
old BSSnew BSS
old routing
newrouting
GSM: handoff with common MSC
§ handoff goal: route call via new base station (without interruption)
§ reasons for handoff:• stronger signal to/from new
BSS (continuing connectivity, less battery drain)
• load balance: free up channel in current BSS
§ handoff initiated by old BSS
7-32Wireless and Mobile Networks
Mobile Switching
Center
VLR
old BSS
1
3
24
5 6
78
new BSS
1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs
2. MSC sets up path (allocates resources) to new BSS
3. new BSS allocates radio channel for use by mobile
4. new BSS signals MSC, old BSS: ready 5. old BSS tells mobile: perform handoff to
new BSS6. mobile, new BSS signal to activate new
channel7. mobile signals via new BSS to MSC:
handoff complete. MSC reroutes call8 MSC-old-BSS resources released
GSM: handoff with common MSC
7-33Wireless and Mobile Networks
We are done!
4-34
That was a lot
§ Now we know how the Internet works, at all layers, in detail.
§ We learned an excellent example of “how to design a system”. Many useful ideas for any future system design problems you might encounter.
§ And there is still a lot more, if you want to go even deeper.
4-35
Final Exam Review
4-36
4-37
Types of Questions
§ Very similar format to the midterm.§ Short answer• Explain some concepts concisely• Simple calculation• Identify the name of a concept based on its description
§ Longer answers• calculations• draw pictures (routing, diagram, etc)• analyze protocol• design protocol• tracing algorithm / procedure• mathematical proof
4-38
Review notes§ Posted on the course website.§ Review so that you can answer all the questions
in the notes.§ Particularly important concepts that require
deeper and detailed understanding are highlighted (boldface and larger fonts)
§ Ideas of possible exam questions to be asked.
4-39
Review Tips§ Understand, don’t memorize.§ How to review• Go through the review notes while going through
lecture slides• Go through tutorials carefully.• Review what you did in assignments.• More exercises:
• past UTM exams (most questions are relevant)• exercises from the textbook.
• Whenever in doubt, ask on the discussion board or come to office hours!
4-40
Pre-Exam Office hours
§ Monday, April 8, 3-5pm§ Wednesday, April 10, 3-5pm§ Friday, April 12, 3-5pm
§ Use them!
4-41
Exam Tips
§ Check the time table. Be there on time!§ Aid sheet allowed: one 8.5x11 double-sided.§ Bring your student card.§ If need any clarification about the questions, raise
your hand and ask.§ Relax and just be yourself.
4-42
A bit more motivation
§ Sticker if get A or A+.
4-43
See you in office hours!
4-44